New research incorporates a single pixel into contact lenses, paving the way for array displays

In Terminator and other sci-fi flicks, robots are often equipped with high tech displays, which pipe text and graphics over human-like views of the world around them. The question some creative researchers have asked is -- why can't humans do that with digitally active contact lenses?

I. The Rise of Digital Contact Lenses: From the Lab to the Marketplace

Want to pipe a digital image into the eyes? You have two possibilities. One is to replace the eyeball with a digital image sensor, which can have its own built in image generating/processing capabilities and pipes finished signals directly into the optical nerve. A lot of work has been done in this field in hopes of giving those blinded by ocular damage vision, but barring "eyeball replacement" surgery, it doesn't do the majority of mankind much good.

A more ubiquitous solution is to develop a contact lens capable of similar feats (e.g. text/images display, biomonitoring, vision magnification, etc.). Think of the active contact lens as a contact on steroids.

It's hard to trace the active contact lens' birth date, but the year might be 1973.

That year James Kinn and Richard Tell, resarchers at the National Environmental Research Center -- a U.S. Environmental Protection Agency lab -- created [abstract] a contact lens with a thermocouple built in. The sensor-cum-contact was arguably the first digitally active design to be realized.

[Image Source: IEEE Transactions on Biomedical Engineering/EPA]

As the electronics revolution commenced in the 1970s and 1980s, though, little work was done to expand on this precocious design. Interest revived in the late 1990s [1][2], but it was not until 2001 that the device would begin to step from concept into commercial reality.

In 2001 Matteo Leonardi (first author; Université de Genève Medical School, Switzerland), Daniel Bertrand (senior author; Université de Genève Medical School, Switzerland), reported that they had used micro-electro-mechanic sensors (MEMS) to create a contact lens that monitored ocular pressure -- an important indicator of Glaucoma. The research was presented at the New Directions in Cellular and Tissue Biomechanics conference in Les Diablerets, Switzerland.

The finished design, dubbed "Triggerfish", uses an embedded a MEMS strain gauge sensor and microprocessor inside a soft silicone contact lens. All of these circuit elements are excentric, out of the line of sight. The device receives power from and ferries signals via a circular antenna around the eye socket.

[Image Source: Sensimed]

II. Next up: Text

In the last decade others have also jumped into this hot field, devising even more ambitious designs. Among the most noteworthy is Professor Babak Parviz of Seattle's Washington University, who added pixel displays to the mix.

Professor Parviz first revealed his current work in 2008 when he presented [abstract] at the Institute of Electrical and Electronics Engineers' international conference on Micro Electro Mechanical Systems a research report.

At the time his system consisted of a single crude light-emitting diode (LED). Since then, he has refined the design, with better LEDs, including the addition of wireless power concepts of Triggerfish (the original '08 design had physical wires powering it) and lower power/smaller LEDs (a 2010 publication [abstract] lists the current consumption at 12 µW).

He's also played with the idea -- perhaps inspired by Triggerfish -- of adding medical sensors, such as a glucose sensor (monitoring tear glucose, an indicator of blood sugar in diabetics), into the design. The work was published [abstract] in Feb. 2011.

The single pixel improved designs is seen in the top three images, while the glucose sensing design is seen at the bottom. [Source: University of Washington]

But creating a contact lens display has been his chief objective. A major obstacle has been focusing the image. In short, you need miniature lenses to focus the image on the eye.

In his latest work Professor Parviz recruited the help of researchers at Finland's Aalto University to create an optimized contact lens which incorporates micro-Fresnel lenses to focus light from the micro LEDs on the retina. The design was tested and proven safe on rabbits, producing no short-term corneal damage

Take a look at the results:

The latest contact (left) is shown in a rabbit's eye, with the LED. Next to it (right) is a microscopic view of the driver circuit (seen in the top-left figure, packaged).
[Image Source: University of Washington]

III. A Work in Progress

Based on that you might notice some problems.

You might think the size of the IC was a problem, but remember you have approximately the area of the iris, minus the incident appr. 100 degree field of view angle from the edge of the pupil -- quite a lot of space, particularly if you're using stacked circuits.

The actual major problem is the wires themselves. While it might be possible to use transpare conductors, the big issue is the wire thickness. A related issue is the short range of the current wireless power transmission.

The paper describes:

Signicant improvements are necessary to produce fully functional, remotely powered, high-resolution displays. Although we could power our system in free space from more than a meter, operating distances on the rabbit eye were reduced to the cm range. Matching, interface and absorption losses are likely causes of the limited operational distance. We are working to improve matching losses, to ensure that power received by the contact lens is maximized at the frequency of best antenna-to-chip matching, and to optimize LED ef?ciency and duty cycling to reduce power consumption of individual pixels. Although only microwatts of power is available on the contact lens, most light generated by the optical components directly enters the eye. Thus, the display could ef?ciently generate an image while consuming little power.

IV. The Future of Digital Contacts

A 32x32 display using OLEDs was recently showcased [white paper] by a startup named Semprius. The display drew approximately 33 mW of power on average, with a 2 µW per-pixel cost (roughly in line with the U of W results, given that many pixels are off).

Semprius makes what may be a solution to the power issue -- thin film micro-solar cells [white paper], which could provide a localized alternative to wireless power distribution.

The cornea is approximate 1.5 cm2 in the average human [source]. A contact lens has an average surface area of around 2-2.5 cm2. Assuming 1,000 W/m2 in full sunlight, this implies an average 0.2-0.25 watts striking the eye. When taking into account, the non-direct incident angle, this likely drops to under 100 mW [source]. Thus such a solution would likely have to include a gel coat that hugs the conjuctiva (white part of the eye) with additional capacity.

Assuming your total exposure for this combined module was 300 mW on a sunny day, your cells would have to be 10 percent efficient to power the Semprius display. Semprius and other startups make micro-solar cells in this efficiency range. Of course these are just crude calculations so they may be a bit off (disclaimer).

The point is that stand-alone low-resolution displays may be able to be powered by the light that the conjuctiva and corneal regions are exposed to, particularly if paired with thermocouples (drawing energy from the body heat) and piezoelectrics (drawing energy from body movement). Alternatively advances in wireless power could lead to safe, longer range power sources.

Ultimately the digitally active contact lens of the future aims to be a high resolution display, which can assert an augmented reality, including text and images over human vision. Such a design would work for business (work displayed right in your eyes), communications (text messages, emails), and pleasure (imagine watching movies or "tripping" without drugs via in-eye vision).

The lens will also likely optionally incorporate glucose, occular pressure, and possibly other sensors to monitor eye health and overall body health.

In terms of text display, Professor Parviz is fast approaching that goal. In an interview with BBC News he states, "Our next goal is to incorporate some predetermined text in the contact lens."

In other words, it may be a few decades before the perfected "iEye" is released commercially, but in just 10 years we may have crude commercial contact lens text displays, if you're willing to wearing a bulky wireless power device around your eye socket.